The present invention relates to ultrasonic leak detection and more particularly, but not exclusively to a method of testing an internal combustion engine and apparatus therefor.
It is known to use ultrasonic waves which pass freely through air gaps to show where such a gap occurs. For example in pressurised or evacuated pipe systems, ultrasonic tests may be carried out at flange joints to detect a leaking gasket and at other points in the system to locate hair-line fractures for example. If pipe pressure or vacuum is sufficiently high then a leak may create its own ultrasonic or sonic waves and an ultrasonic detector may be used to locate the fault.
In an alternative method, ultrasonic generators may be used to inject ultrasonic signals into the system particularly where the internal pressure or vacuum is not sufficient in itself to cause a leak to go ultrasonic. Escaping ultrasonic signals may be detected as before to enable determination of necessary remedial action.
The physical size of presently available ultrasonic signal generators inhibits their use in many applications. Furthermore, where multiple leakage paths may occur, it may be difficult to determine where a leak is occurring. Considering a specific example with regard to an internal combustion engine, if say two adjacent cylinders of the engine have a leakage path between them then the leak may be by way of a head gasket fault, through an inlet valve or through an exhanust valve for example.
It will also be noted that an engine is not a stable system--that is to say that gas pressures are constantly varying in differing parts thereof. Thus unstable readings are obtained in dependance upon the relative position in the cycle of the engine. Leak detection without running the engine is accordingly extremely difficult whilst with the engine running, exhaust leaks, ignition systems, fuel injectors and general background ultrasonic signals (for example from bearings) all interfere with ultrasonic leak detection.